Automotive cooling systems often employ cooling fans which are driven by electric motors and this requires that the fan be physically attached to the motor in some manner. Such cooling fan and motor systems or modules are desirably relatively compact, with the axial length of the fan and motor assembly desirably minimized in order to be accommodated in the ever-decreasing design space allocated under the hood of a modern automobile. Another imperative in the automotive industry is to reduce manufacturing costs through simplification of parts fabrication and assembly. In an effort to maximize fuel economy, it is also desirable to reduce the weight of the fan and motor assembly wherever feasible. As persons skilled in the art will appreciate, endeavoring to minimize size, weight, noise and vibration during the life cycle of a cooling fan module as well as reducing manufacturing costs, while simultaneously endeavoring to enhance reliability, often presents conflicting design parameters, and ultimately design choices.
Previously known cooling fan and motor assemblies have attached the fan to the motor shaft with radial spring clips, similar to belleville washers, which provided axial tension to secure the fan to the shaft. The spring clip typically engaged the shaft via a groove formed in the shaft. Over the life cycle of the fan and motor, the spring clip could have fatigued and thereafter broken, thus causing separation of the fan from the motor shaft. The addition of a spring clip attachment system to a fan and motor assembly also inherently increased the axial length of the assembled structure. Furthermore, the spring clip did not readily inhibit a rocking of the fan relative to the motor shaft because: (a) the spring clip typically flexed in response to rocking loads on the fan, and (b) the relatively small diameter of the spring clip did not provide a sufficiently large bearing surface to counteract rocking loads on the fan.
Another known attachment system for cooling fans and motor shafts involved molding a metal hub within the fan. The metal hub was then attached to the motor shaft via a pin, such as a roll pin. Although this molded-in-place hub and pin attachment system provided an effective and reliable fan connection, it increased the manufacturing complexity of the cooling fan modules in a number of ways. First, the motor shaft was drilled to receive the pin. Second, plastic fans which included molded-in-place metal hubs were inherently more expensive to manufacture than fans which were only constructed of plastic. Third, the fan and motor assemblies which required insertion of pins added additional manufacturing assembly steps.
Hence, it remains a challenge in the automotive industry to provide a cooling fan module or unit which has a compact structure (e.g. a compact axial length of the assembly) and which maintains both reliability and good dynamic balance (e.g. low vibration and noise) over the life cycle of the product, but which is nevertheless relatively inexpensive to manufacture and assemble.